Materials for making spark plug electrodes for internal combustion engines, for example, automotive engines. are required to have high strength at elevated temperatures, high melting loss resistance, high corrosion resistance at elevated temperatures, and high spark consumption resistance.
An Ni alloy having these properties as described in, for example, Japanese Patent Publication No. 43897/85 (corresponding to U.S. Pat. No. 4,329,174) has conventionally been used in spark plug electrodes and consists essentially of, on a weight percent basis, 0.2 to 3% Si, less than 0.5% Mn, at least two elements selected from the group consisting of 0.2 to 3% Cr, 0.2 to 3% Al and 0.01 to 1% Y, and the balance Ni and incidental impurities.
On the other hand, since the temperature of the combustion chamber atmosphere is greatly elevated in recently developed engines due to their high rotational speeds and the use of high octane value petroleum, the spark plug electrodes are exposed to very high temperature combustion atmospheres.
Although the conventional Ni base alloy described above exhibits good melting loss resistance, corrosion resistance at elevated temperatures and spark consumption loss in high temperature combustion atmospheres, its strength at elevated temperatures is not adequate. Accordingly, spark plug electrodes made of such a conventional Ni alloy cannot withstand practical use for long periods of time under such harsh operating conditions and the life of conventional electrodes is naturally rather short.